In the fields of measurement or calibration, a standard inductance box (or set of inductors) is a special inductance instrument to ensure the conformity of inductance, as a standard value to transfer inductance parameters in AC parameter measurement.
In the inductance parameter measurement, the current standard inductance boxes made in China or foreign countries are decimal inductance boxes. The standard inductance box with the widest range has six series of tenfold decimal inductance box with a range from 1 μH to 1 H, which has 60 output selections of inductance values in total. However, it has disadvantages such as limited measuring range, large size, and heavy weight. Thus, it cannot achieve the whole measuring range, and it is inconvenient for field applications and transport. As to development towards future demands, the existing measurement range from 1 μH to 1 H cannot meet the requirements for inductance unit transfer and calibration. Therefore, it is required to develop a novel standard inductance box with wider range, e.g. from 1 μH to 500 H.
A standard inductance box mainly comprises standard inductors, a change-over switch, output connectors, and chassis, etc. Standard inductors may be divided into actual inductors and analogous inductors (passive). Relatively stable actual inductors are coil wound inductors, which usually have inductance from 1 μH to 1 H, and the max inductance of 10 H. However, the large value inductors have big size and heavy weight, and are inconvenient for field application. An analogous inductor is a T-type equivalent circuit. It can achieve the inductance range from 100 mH to 10000 H. Existing analogous inductors have usually single-value inductance. Current inductance boxes are made of actual inductors with the values in decimal steps from 1 μH to 1 H. In order to realize the wider inductance range in RLC digital bridge, a new standard inductance box is developed with a novel and compact design, that is light weight, and has a much wider inductance range.